When the price elasticity of supply is equal to zero..................

Supply curve is vertical.

The correct answer is Option (4) → Supply curve is vertical.

Price Elasticity of Supply (PES) measures how much the quantity supplied changes in response to a change in price.

• When PES = 0, it means that no matter how much the price changes, the quantity supplied remains constant.

• This is called perfectly inelastic supply.

• A vertical supply curve represents this situation — quantity supplied is fixed, and does not respond to price changes.